Kindlin-3 interacts with the ribosome and regulates c-Myc expression required for proliferation of chronic myeloid leukemia cells

Jing Qu,Srikanth Nama,Hui-Shan Lee,Muhammad Hb Ismail,Hui-Foon Tan,Yong-Gui Gao,Li-Teng Ong,Prabha Sampath,Chen Feng,Rya Ero,Suet-Mien Tan,Wen-Ting Bu

doi:10.1038/srep18491

Abstract

Kindlins are FERM-containing cytoplasmic proteins that regulate integrin-mediated cell-cell and cell-extracellular matrix (ECM) attachments. Kindlin-3 is expressed in hematopoietic cells, platelets, and endothelial cells. Studies have shown that kindlin-3 stabilizes cell adhesion mediated by ß1, ß2, and ß3 integrins. Apart from integrin cytoplasmic tails, kindlins are known to interact with other cytoplasmic proteins. Here we demonstrate that kindlin-3 can associate with ribosome via the receptor for activated-C kinase 1 (RACK1) scaffold protein based on immunoprecipitation, ribosome binding, and proximity ligation assays. We show that kindlin-3 regulates c-Myc protein expression in the human chronic myeloid leukemia cell line K562. Cell proliferation was reduced following siRNA reduction of kindlin-3 expression and a significant reduction in tumor mass was observed in xenograft experiments. Mechanistically, kindlin-3 is involved in integrin α5ß1-Akt-mTOR-p70S6K signaling; however, its regulation of c-Myc protein expression could be independent of this signaling axis.

Highlights

Kindlins are family of 4.1-ezrin-radixin-moesin (FERM)-containing cytoplasmic proteins that regulate integrin-mediated cell-cell and cell-extracellular matrix (ECM) attachments
receptor for activated-C kinase 1 (RACK1) forms a complex with focal adhesion kinase (FAK) and phosphodiesterase 4D5 (PDE4D5) that mediates direction sensing in migrating cells[33]
We ruled out the possibility of non-specific interactions as these ribosomal proteins were not detected in immunoprecipitation samples using the same mAb but with cell lysate of human kidney fibroblast 293T that does not express kindlin-3

Summary

Introduction

Kindlins are FERM-containing cytoplasmic proteins that regulate integrin-mediated cell-cell and cell-extracellular matrix (ECM) attachments. Studies have shown that kindlin-3 stabilizes cell adhesion mediated by ß1, ß2, and ß3 integrins. Kindlins are a small family of 4.1-ezrin-radixin-moesin (FERM)-containing cytoplasmic proteins that regulate integrin activation and outside-in signaling[1,2,3,4]. Kindlins bind to the membrane distal NxxY/F motif of the ß integrin cytoplasmic tails[10,12]. RACK1 is ubiquitously expressed in all tissues and it is a Trp-Asp (WD) 40 ß-propeller cytoplasmic protein[25,26] It has many binding partners, including activated protein kinase C (PKC), c-Src, G protein ßγ subunits, as well as ß1, ß2, and ß5 integrin cytoplasmic tails[27,28,29,30]. It has been shown to promote internal ribosome entry site (IRES)-mediated translation of hepatitis C viral proteins[37]

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Results

Conclusion